Dishwashing machines, particularly commercial types (for bars, restaurants, communities, etc.), normally comprise a front-loading wash tub closed in use by a swing door, e.g. rotating about a horizontal axis at the bottom edge of the door. The door therefore swings downwards and, in the fully open position, is substantially horizontal (or at most slightly tilted), so the inner face of the door also acts as a support for the dish-rack when this is extracted from the wash tub.
Doors of dishwashing machines of this type may be relatively heavy, and are opened frequently in use, either to load and unload the machine or check the dishes during the wash cycle, so the door is equipped with a counterbalancing device to at least partly counterbalance its weight and make it easier for the user to open and close. The machine must also be equipped with a pressure locking system to lock the door in the open and closed positions and preferably also in an intermediate, partly open position, to allow the steam to escape and to partly cool the dishes before they are unloaded.
CH-A-683886 describes a dishwashing machine in which the weight of the door is counterbalanced by a coil spring, which is stretched when the door is opened and so also assists the user in closing the door; and the door is locked, at least in the two limit positions, by a system of arms having limit stops and interconnected by a pin sliding inside a slot. The door can also be locked in the closed position by a pull-release spring lock.
Similar door braking and/or stop devices are also described in DE-A-19958817 and WO2006117893. In the latter, the coil spring operates together with a complex system of levers connected to an extremely bulky threaded rod housed partly inside the thickness of the door.
In other words, known dishwashing machine door counterbalancing devices are bulky, complicated, frequently unreliable (e.g. due to jamming of the levers), and do not always provide for locking the door in the closed position, so the machine must also be equipped with an additional locking device.